The present invention relates to a semiconductor device, and more specifically to a method for manufacturing a capacitor in semiconductor device wherein the thin walls of the lower electrode of the capacitor can be protected from damage during etching without compromising the alignment process.
In general, a process for forming a capacitor is performed with an oxide film as a sacrificial layer for forming a lower electrode.
FIGS. 1a through 1e are cross-sectional diagrams illustrating a method for forming a lower electrode of a conventional capacitor.
Referring to FIG. 1a, an interlayer insulating film 10, including a lower electrode contact plug 20, is formed over a semiconductor substrate (not shown). Then, an etching stop film 30 and a sacrificial oxide film 40 for forming a lower electrode are formed over the interlayer insulating film 10. Next, a photoresist film pattern 70 for making the storage electrodes is formed over the sacrificial oxide film 40.
Referring to FIG. 1b, the sacrificial oxide film 40 and the etching stop film 30 are etched with the photoresist film pattern 70 as an etching mask to form the lower electrode region 80.
Referring to FIG. 1c, a lower electrode material 90 is formed over the entire surface of the semiconductor substrate including the lower electrode region 80.
Referring to FIG. 1d, the lower electrode material 90 formed on the top surface of the sacrificial oxide film 40 is removed so that only one lower electrode 95 is connected to each lower electrode contact plug 20.
Referring to FIG. 1e, a wet etching method is performed to remove the sacrificial oxide film 40. After a dielectric layer (not shown) is formed over the surface of the lower electrode 95, a plate electrode layer (not shown) is formed over the entire surface of the semiconductor substrate to complete the capacitor. However, the lower electrode 95 can collapse during the wet etching process of the sacrificial oxide film 40.
The use of an amorphous carbon layer can prevent the collapse of the lower electrode 95. However, amorphous carbon has high optical absorbance that can impede the alignment process of the lower electrode contact plugs and the photoresist film pattern.
FIG. 2 is a cross-sectional diagram illustrating an alignment mark when an oxide film is used as a sacrificial layer.
Referring to FIG. 2, an alignment mark 35 and a predetermined number of alignment keys 25 are formed in an outer region of a semiconductor substrate. Here, the alignment key 25 is formed over the interlayer insulating film 10, and the etching stop film 30 and the sacrificial oxide film 40 are deposited thereon.
Thereafter, light is irradiated into the alignment key 25 to perform an alignment process using the diffracted light so that the lower electrode contact plug and the photoresist film pattern are aligned. Here, light is easily penetrated and diffracted in the sacrificial oxide film and the etching stop film because they have low optical absorbance. As a result, it is easy to perform the alignment process. However, when the sacrificial oxide film is substituted with the amorphous carbon layer, light does not pass through (or is diffracted) but gets absorbed in the amorphous carbon layer. As a result, it is difficult to perform the alignment process.
FIG. 3 is a cross-sectional diagram illustrating an alignment process when an amorphous carbon layer is used as a sacrificial layer.
Referring to FIG. 3, the sacrificial oxide film of FIG. 2 is substituted with the amorphous carbon layer 45 and an alignment mark is formed, then a hard mask SiON film 50 is formed over the amorphous carbon layer 45. In this case, although the SiON film has low optical absorbance, the amorphous carbon layer 45 has high optical absorbance. As a result, much of the light is absorbed by the amorphous carbon layer 45 and a very little amount of light passes through the amorphous carbon layer 45. This makes it difficult to perform an accurate alignment process, particularly during the process of forming capacitors.